In a multi-sector communication system including a plurality of sectors, limited resources including frequency resources, code resources, and time slot resources are divided and used among the sectors. Since the same resources are reused by other sectors, interference can result between the sectors, particularly neighboring sectors. However, although the interference attributable to the reuse may cause performance degradation, it may also increase the entire capacity of the multi-sector communication system. The interference is severe when a frequency reuse factor is 1.
Meanwhile, a next-generation communication system is being actively studied for providing users with services with high quality of service (“QoS”), such as high transmission speed. In particular, a base station (“BS”) in the next-generation communication system divides and manages one cell into a plurality of sectors. When providing communication service to mobile stations (“MSs”) located in the plurality of sectors, the BS transmits data to the MSs via respective sector antennae. Here, the BS transmits the data to the MSs using beams from the sector antennae, which overlap at a boundary between the sectors. This causes interference between the sectors.
More specifically, the use of the sector antennae in the multi-sector communication system causes inter-sector interference in a signal overlap region between sectors, i.e., a inter-sector boundary region. In other words, since patterns of beams from the sector antennae cannot be designed to be orthogonal to one another, signals from neighboring sectors overlap in the inter-sector boundary region, which causes severe interference between the sector signals, that is, between the neighboring sectors.
A current communication system fails to avoid and minimize such inter-sector interference, and exhibits low reuse efficiency of frequency resources when attempting to avoid and minimize the inter-sector interference. Accordingly, there is a need for a system and method for using resources that are capable of avoiding inter-sector interference in a signal overlap region between sectors by allocating a central band orthogonal between the sectors to a inter-sector boundary region where signal overlap may occur, and greatly improving the reuse efficiency of frequency resource by allowing remaining frequency resources to be reused without inter-sector interference in sector central regions where there is no inter-sector interference.
Also, there is a need for a system and method capable of preventing signal quality from being degraded by rapid reduction of antenna gain in a inter-sector boundary region that may be caused by signal transmission or reception in the inter-sector boundary region to or from one sector for avoidance and minimization of inter-sector interference in the inter-sector boundary region. Also, there is a need for a system and method capable of providing sufficient time to perform stable dynamic channel allocation (“DCA”) and guaranteeing stable QoS so that several DCAs are performed at a high speed upon inter-sector handover of MSs in a plurality of sectors of a communication system. In particular, there is a need for a system and method capable of preventing a system load from increasing due to a ping-pong phenomenon upon frequency movement in a inter-sector boundary region, on a sector central boundary line, from a inter-sector boundary region to a sector central region, or from the sector central region to the inter-sector boundary region.
In other words, in the inter-sector boundary region, signal gain greatly decreases due to rapid reduction of the antenna gain, resulting in degraded signal quality. Also, when a user moves via a sector boundary line, signal quality degradation becomes severe. This requires rapid handover to a neighboring sector, and accordingly, rapid DCA from a current sector band to another band and to a neighboring sector band. This leads to signal quality degradation and QoS degradation, and causes a ping-pong phenomenon, resulting in an increase in a system load. Thus, there is a need for a system and method for solving the problems. That is, there is a need for a system and method capable of avoiding and minimizing inter-sector interference in a inter-sector boundary region of a multi-sector communication system, simplifying a handover procedure while maintaining signal quality, and increasing reuse efficiency of the frequency resource.
Accordingly, the present invention allocates used bands and bands reused in all sectors to be orthogonal among the sectors in order to avoid and minimize inter-sector interference in a inter-sector boundary region and efficiently use frequency resources. Also, there is a need for a method and system for using resources that are capable of entirely avoiding and minimizing inter-sector interference by allocating a specific band of each sector to users located in a boundary region of the sector and by reusing a band allocated to be reused in all sectors where inter-sector interference is not considered or there is no inter-sector interference.
When an MS moves between sectors, band allocation is made based on a signal power ratio between neighboring sectors. When a user, i.e., an MS allocated a band in a current sector moves to a inter-sector boundary region, a BS serving the MS performs DCA to a band for the current sector, thus avoiding and minimizing the inter-sector interference. In this case, the present invention prevents signal quality degradation caused by rapid antenna gain reduction in the inter-sector boundary region in handover between sectors. In particular, the present invention prevents signal quality degradation caused by performing rapid handover to a neighboring sector with the intention of preventing rapid signal intensity degradation when an MS moves between sectors, i.e., performing rapid DCA to a band for a neighboring handover sector, and avoids and minimizes the inter-sector interference.
Also, movement of an MS to a neighboring sector requires DCA to a band for the sector, which degrades signal quality in a inter-sector boundary region and in turn necessitates several rapid DCAs. Accordingly, the present invention provides sufficient time to perform stable DCAs and guarantees QoS. Moreover, the present invention prevents a ping-pong phenomenon from being caused by frequent inter-sector handover, e.g., frequent movement between regions in a sector, and particularly, simplifies a DCA procedure and a handover procedure in more frequent and rapid movement between sectors in a cell central region, thus reducing a system load.